The invention concerns a switch for controlling a control current for the control of an operating current of electric motors in linear transmissions, for example for the actuation of sick-beds, tables or the like. Such switches comprise a switch housing having at upper part including buttons and a lower part for forming a receiving space. Received in the receiving space is a circuit board having microswitches which have a switch housing and a spring-biased pushrod therein. Upon actuation of the buttons by a user the elastic or resilient button is depressed on to the pushrod of the microswitch and thus actuates the microswitch for controlling the control current. In addition such a hand switch has at least one locking device which can be displaced by the user from a locking position of locking the button into a release position of releasing the buttons.
Such switches which are in the form of hand switches are known for example from EP 0 480 221 B1 and WO 2005/036576. Both specifications are concerned with the problems of mechanical locking devices for the buttons in a hand control or a hand switch. Those hand switches include one or more buttons in an upper part which is connected to a lower part. Provided between the upper part and the lower part is a receiving space in which there is arranged a circuit board on which microswitches are fixed. Those microswitches have a spring-biased button arrangement which is depressed upon actuation of the buttons of the upper casing part and thus controls the control current for actuation of the operating current for the electrically operated drive or drives. Usually the two respective buttons are arranged in juxtaposed paired relationship in order to respectively permit the two opposite modes of operation for a respective electric motor.
The proposed solutions propose locking devices which are rotatable about a central axis and which can be rotated from the release position into the locking position. In the locking position the locking devices block the buttons to prevent them from being depressed in the upper part on to the pushrods of the microswitches. They therefore bear in contact between the underside of the elastic buttons and the upper part of the housing of the microswitch in such a way that it is not possible for the buttons to be pressed down on to the pushrod of the microswitch. In the rotated release position the two laterally projecting locking arms of the locking device free that arresting action and allow the buttons to be pressed down on to the microswitches.
EP 0 480 221 B1 operates with pneumatic switches, but with a similar principle with a rotatable locking device which in the locking position prevents the buttons from being pressed down by engagement at one side into the opening. That has the disadvantage that the one-sided displacement can cause tilting of the buttons. WO 2005/036576 discloses a further configuration of a mechanical locking arrangement.
Those mechanical locking arrangements transmit the locking forces to the microswitch and to the circuit board on which the microswitch is soldered. In ongoing operation that can result in destruction of the microswitch and/or the solder joints, and that then results in a system fault.